The present invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to a developer composition comprised of carrier, and toner containing a polyester with both hydrophilic and hydrophobic groups and wherein the main chain of the resin contains a hydrophilic moiety, that is, for example, wherein moiety refers to a group or groups on the main polymer chain in an amount of, for example, from about 0.5 to about 3 percent based on the amount of toner polyester polymer, or parts which, for example, impart or assist in imparting excellent triboelectrical and with rapid admix characteristics, and wherein the end groups of the polyester resin are modified with or contain hydrophobic moieties, groups, or segments, preferably two, present in an amount of, for example, from about 0.5 to about 2 percent or parts based on the amount of polyester polymer to, for example, impart or assist in imparting excellent relative humidity sensitivity to the toner. In embodiments, there are provided in accordance with the present invention toner compositions comprised of colorant particles, and resin particles comprised of a polyester resin containing hydrophilic moieties such as a sodio sulfonate group or groups, in an amount for the moieties, groups, or segments of, for example, from about 0.5 to about 3 weight percent of the polyester resin or polymer and preferably from about 1 to about 2 weight percent of the resin, and hydrophobic, that is for example nonpolar, or nonwater liking groups such as alkyl, alkylene, with, for example, from 6 to about 120 carbon atoms, such as hexyl, lauryl, stearyl, cetyl, polyethylene, polypropylene and the like. More specifically, in embodiments of the present invention, there is provided a toner comprised of colorant, especially pigment particles, optionally a charge enhancing agent, optionally a wax component, and a polyester resin containing both a hydrophilic moiety on the main chain, and hydrophobic end groups, and which polyester is illustrated by Formulas I through III ##STR1## wherein R is an alkylene group, such as a divalent ethylene, propylene, butylene, ethyleneoxyethylene or generally a hydrocarbon, with from about 2 to about 24 carbon atoms, from about 2 to about 22, and preferably from about 2 to about 20 carbon atoms, and more specifically, with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22 carbon atoms; a cycloalkylene like cyclohexylene or a 1,4-dimethyl cyclohexylene group; X is an aromatic, such as an arylene group, with, for example, from about 6 to about 14 carbon atoms, such as the moieties of phenylene, isophthalylene, terephthalylene or phthalylene, an olefinic group (or groups throughout), such as vinylene, methylvinylene, or an alkylene group such as ethylene, propylene, butylene, pentylene, hexylene, and the like; R' is a hydrophobic group or groups, such as an alkyl group with, for example, from about 2 to about 120 carbon atoms, such as hexyl, heptyl, octyl, lauryl, stearyl, alkylene, such as polyethylene or polypropylene; and m and n represents the number of random segments, such as a number of from about 10 to about 100 for n and about 20 to about 2,000 for m or 20 times n; S is a hydrophilic group, such as an alkali earth metal salt of an arylenesulfonate or alkylenesulfonate, and more specifically, an alkaline earth metal such as lithium, sodium, potassium, cesium, berylium, magnesium, calcium or barium, an arylenesulfonate such as phenylenesulfonate, isophthalylene-5-sulfonate, terephthalylene-sulfonate or phthalylenesulfonate, or an alkylenesulfonate such as propylenesulfonate, butylenesulfonate, pentylenesulfonate, hexylenesulfonate; and Y can be either X or S. The polyester resin can be branched or crosslinked by employing trifunctional or multifunctional reagents, such as trimethylolpropane or pyromellitic acid, in an amount of, for example, from about 0.1 to about 6 mole percent based on the starting diacid or diester selected to prepare the polyester resin, and which branching agent can be represented in the above Formulas I through III by incorporating the branching segments, p, q, r or s as illustrated by the formulas ##STR2## wherein R" is a multivalent aromatic radical with, for example, from about 6 to about 30 carbon atoms, or an aliphatic radical with from about 3 to about 20 carbon atoms, such as the tri or tetravalent derivatives of propane, butane, pentane, hexane, cyclohexane, heptane, octane, benzene, naphthalene, anthracene, and the like; and p, q, r and s represent the branching segment and in embodiments each is from about 0.1 to about 6 mole percent based on the starting diacid or diester used to generate the resin and provided that the sum of segments p and q, or r and s is 100 mole percent of the polyester resin.
In embodiments, the present invention relates to the preparation of a polyester resin, and wherein the hydroxyl and acid end groups of the resulting polyester are minimized, and preferably avoided. Polyester resins are known to contain acid and hydroxyl groups of from about 20 to about 1,000 milliequivalents per gram of polyester, usually present as end groups. It is believed that these hydrophilic end groups may cause the toner composites to possess tribocharging performance that is humidity sensitive, wherein the ratio of the triboelectric charge of the toner composites at low humidity to that at high humidity is of from about 2.8 to about 4.5, and usually from about 3.0 to about 3.5. To reduce the relative humidity sensitivity of polyester based toners, the present invention minimizes the hydrophilic end groups, such as hydroxyl or acid moieties on the polyester resin, by capping the ends of the polyester with hydrophobic groups, such as alkyl moieties, hence resulting in toners with low humidity sensitivity in embodiments such as from about 1.0 to about 2.8 and preferably from about 1.0 to about 2.5.
Another embodiment of the present invention relates to the obtaining toner composition with excellent triboelectrical stability and rapid admix such as less than about 1 minute and preferable less than about 30 seconds, for example from about 5 to about 15 seconds, and which toner contains a polyester resin with a hydrophilic moiety, such as a sodio sulfonate group, present on the main chain of the resin. A further embodiment of the present invention relates to the preparation of a polyester resin with monofunctional monomers that cap the ends of the polyester resin to result in the aforementioned polyester resin with hydrophobic end groups, and wherein the concentration of the monofunctional hydrophobic monomers is from about 0.1 mole percent to about 4 mole percent based on the starting diacid or diester used to generate the resin, and thereby controls the weight average molecular weight of from about 4,000 grams per mole to about 250,000 grams per mole, especially when monofunctional monomers with a carbon chain length of from about 4 to about 24 are selected or wherein the use of bulkier monomers such as 1,2-naphthalene ethanol, or phenylmethanol are utilized; and wherein a hydrophilic moiety such as sodio sulfonate group is present in the main chain of the polyester resin, and wherein the concentration of the hydrophilic moiety is from about 0.1 to about 5 weight percent of the resin, and preferably of from about 0.5 to about 2.5 weight percent of the resin.
The aforementioned toner composition and developer thereof, that is toner mixed with a carrier, display a low relative humidity sensitivity for the toners in embodiments of the present invention, which is desired since the triboelectric charge remains stable with changes in environmental humidity conditions. Additionally, the toners possess rapid admix characteristics, such as less than about 60 seconds, and preferably less than 30 seconds, for example from about 5 to about 15 seconds, and low minimum fixing temperatures, such as from about 130.degree. C. to about 145.degree. C., with broad fusing latitudes, such as from about 30.degree. C. to about 90.degree. C. Copiers and printers equipped with two component developers, that is a toner as one component mixed with the carrier as the other component, can exhibit a positive or negative triboelectric charge with a magnitude of from about 5 microcoulombs per gram to about 40 microcoulombs per grams. This triboelectric charge permits the toner particles to be transferred to the latent image of the photoreceptor with an opposite charge, thereby forming a toned image on the photoreceptor, which is subsequently transferred to a paper or a transparency substrate, and thereafter subjected to fusing or fixing processes. In these development systems, it is important for the triboelectric charge to be stable under differing environmental humidity conditions such that the triboelectric charge does not change substantially by more than from about 5 to about 10 microcoulombs per gram. A change of more than from about 5 microcoulombs per gram to about 10 microcoulombs per gram in the triboelectric charge of the toner developer can cause nonuniform toned images or result in no toning of the photoreceptor, thus unbalanced density or gray scale is observed in the developed images, or no developed images at all result. Generally, humidity ranges may differ from less than about 20 percent in dry regions to more than about 80 percent in humid regions, and some geographical regions may exhibit fluctuations of up to from about 50 to about 90 percent humidity level within the same day. In such climates, it is important that the developmental triboelectric charge does not change by more than from about 5 microcoulombs per gram to about 10 microcoulombs per gram. As toner resins generally represent from about 80 percent to about 98 percent by weight of toner, the resin sensitivity to moisture or humidity conditions should be minimized thereby not adversely affecting the triboelectric charge thereof. Furthermore, the toners should preferably possess rapid admix characteristics, such that when copiers and printers are replenished with fresh toners, the developers can re-establish the necessary triboelectric charge within less than 1 minute, and preferably less than 30 seconds.
A number of toner polymeric resins utilized as toner compositions, such as for example styrene-acrylates, styrene-methacrylates, styrene-butadienes and especially polyesters, contain from about 0.1 to about 2 percent by weight of moisture, and in some instances, the moisture content of polyesters may change from about 0.1 to about 4 percent by weight at humidity levels ranging from about 10 to about 100 percent, or more usually from about 20 percent to about 80 percent humidity. These changes in moisture content of the resin may have a dramatic adverse effect on the triboelectric charge of the toner and developer thereof. Relative humidity sensitivity of toner is customarily measured by first fabricating a toner comprised of a pigment, optional charge control agent and a resin, then admixing the toner from about 3 percent by weight to about 7 percent by weight with a carrier. The developer composition is then equilibrated to various humidity levels in a sealed chamber at controlled temperatures of 60.degree. F. at 20 percent RH and 80.degree. C. at 80.degree. F. for a period of about 48 hours. The triboelectric charge is then measured for the same developer composition at different humidity levels and the results analyzed by several methods, such as graphing the triboelectric charge as a function of humidity level and observing the regions in which dramatic changes occur. Another measuring method comprises dividing the aforementioned graphical interpolation of tribo versus humidity level in three regions, wherein region A is from about 0 to about 30 percent humidity, region B is from about 30 to about 65 percent humidity, and region C is higher than about 65 percent humidity to about 100 percent. Since these measurements are cumbersome and time consuming, there can be measured the triboelectric charge after subjecting the toner developer composition to two humidity levels, such as 20 percent relative humidity and 80 percent relative humidity, and then calculating the relative sensitivity by the triboelectric charge ratio of the 20 to 80 percent relative humidity as follows
Equation 1 ##EQU1## wherein RH is the relative humidity.
Thus, if the relative humidity sensitivity is about 1, the toner composition is considered humidity insensitive, whereas if the humidity sensitivity is greater than about 3, the toner composition is considered to be humidity sensitive. It is generally believed that toners prepared with a number of polymeric materials exhibit relative sensitivity greater than 1.0, and in general, styrene butadiene, or styrene acrylate based toners possess humidity sensitivities greater than 1.0 and less than about 2.5, whereas generally, polyester based toners possess a relative humidity sensitivity of greater than 2.5 and less than about 5. Hence, an advantage of the styrene-acrylate or styrene-butadiene type binder resins for toners over that of polyesters is their lower relative humidity sensitivity. Polyesters are known to display advantages over styrene based resins, such as low fixing temperatures of from about 120.degree. C. to about 140.degree. C., and nonvinyl offset properties. Therefore, there is a need for toner compositions comprised of a resin which possess many of the aforementioned advantages, such as low fixing temperature of from about 120.degree. C. to about 140.degree. C., nonvinyl offset properties, and in addition low sensitivity of tribocharging as a function of relative humidity such that the ratio of triboelectric charge at 20 percent and 80 percent RH is from about 1.0 to about 2.5. These and other advantages are attained in embodiments with the toner compositions of the present invention comprised of a pigment, optionally a charge control agent, and a modified polyester resin wherein the end groups are hydrophobic moieties, and which toner exhibits a low fixing temperature of from about 120.degree. C. to about 140.degree. C., nonvinyl offset properties, and low relative humidity sensitivity, such as from about 1.0 to about 2.5.
Furthermore, the presence of the hydrophobic end groups provide an improved process for obtaining polyesters. Specifically, the concentration of the monofunctional monomer and groups provides for the molecular weight control of the polyester product, and its reproducibility. The process for the preparation of the polyester resins of the present invention is referred to as a condensation process or step polymerization. The condensation process involves the addition of bifunctional monomers which result in dimers, followed by the reaction of dimers with dimers to form tetramers, or dimers with monomers to form trimers. The reaction sequence then continues in that these dimers, trimers and tetramers react with each other to form multiples thereof, known in the art as oligomers, which in turn react with other oligomers to form the polyester. In this kinetic scheme, the degree of polymerization is achieved by terminating the reaction at the desired point, hence it is time dependent. It is known that obtaining a specific degree of polymerization by relying on the time of the polymerization of the step reaction polymerization process is very difficult. A method for controlling the degree of polymerization is to adjust the composition of the reaction mixture away from stoichiometric equivalence, by adding a nonvolatile monofunctional reagent in an amount from about 0.1 mole percent to about 4 mole percent based on the starting diacid or diester used to make the resin. In the present invention, the monofunctional monomers employed are, for example, hydrophobic monomers. The degree of polymerization can further be controlled by the amount of monofunctional monomer utilized, hence limiting the degree of polymerization as determined by its concentration such that the total amount of end groups is proportional to the amount of monofunctional monomer employed. This aids in the reproducibility of the product by adjusting the amount of monofunctional monomer to the desired limit of degree of polymerization, hence avoiding total dependence on time of polymerization.
Additionally, the toner resin of the present invention contains a hydrophilic moiety, such as an alkali salt of a sulfonate group, which group is believed to impart triboelectric stability for long duration, such as from about 250,000 to about 1,000,000 prints or copies, and which function also enables rapid admix times such as less than about 1 minute and preferable less than about 30 seconds.
The toner compositions of the present invention in embodiments thereof possess excellent admix characteristics as indicated herein, and maintain their triboelectric charging characteristics for an extended number of imaging cycles up to, for example, 1,000,000 in a number of embodiments.
There is a need for toners with low relative humidity sensitivity, such as from about 1 to about 2.8 and preferably from about 1 to about 2.5 as calculated by Equation 1, and wherein excellent triboelectric stability is achieved, such as from about 250,000 to 1,000,000 prints or copies, as rapid admix time, such as from less than about 1 minute and preferably less than about 30 seconds, and wherein low minimum fixing temperatures are obtained, such as from about 120.degree. C. to about 140.degree. C. with broad fusing latitude such as from about 30.degree. C. to about 45.degree. C., wherein the fusing latitude is considered the difference between the minimum fixing temperature and the temperature at which the toner offsets to the fusing member. These and other needs can be achievable with the present invention in embodiments thereof.